Sensitivity of the PBP2a SA Culture Colony Test on shortly incubated subcultures of methicillin-resistant staphylococci from positive blood cultures

The sensitivity of an immunochromatographic assay for detecting methicillin resistance (PBP2a SA Culture Colony Test, Alere-Abbott) on shortly incubated subcultures of staphylococci in blood cultures was evaluated. The assay is highly sensitive for the detection of methicillin-resistant Staphylococcus aureus after 4 hour-subculture but requires 6 hour-incubation for methicillin-resistant coagulase-negative staphylococci.

Prevalence, Mechanism, Genetic Diversity, and Cross-Resistance Patterns of Methicillin-Resistant Staphylococcus Isolated from Companion Animal Clinical Samples Submitted to a Veterinary Diagnostic Laboratory in the Midwestern United States

Methicillin-resistant Staphylococcus (MRS) is a leading cause of skin and soft tissue infections in companion animals, with limited treatment options available due to the frequent cross-resistance of MRS to other antibiotics. In this study, we report the prevalence, species distribution, genetic diversity, resistance mechanism and cross-resistance patterns of MRS isolated from companion animal (mostly dog and cat) clinical cases submitted to Iowa State University Veterinary Diagnostic Laboratory (ISU VDL) between 2012 and 2019. The majority of isolates were identified as Staphylococcus pseudintermedius (68.3%; 2379/3482) and coagulase-negative Staphylococcus (CoNS) (24.6%; 857/3482), of which 23.9% and 40.5% were phenotypically resistant to methicillin, respectively. Cross resistance to other β-lactams (and to a lesser extent to non-β-lactams) was common in both methicillin-resistant S. pseudintermedius (MRSP) and CoNS (MRCoNS), especially when oxacillin MIC was ≥4 μg/mL (vs. ≥0.5−<4 μg/mL). The PBP2a protein was detected by agglutination in 94.6% (521/551) MRSP and 64.3% (146/227) MRCoNS. A further analysis of 31 PBP2a-negative MRS isolates (all but one MRCoNS) indicated that 11 were mecA gene-positive while 20 were negative for mecA and other mec genes by PCR. The resistance to last-resort anti-staphylococcal human drugs (e.g., tigecycline, linezolid, vancomycin) among the MRS tested was none to very low. Even though genotyping indicated an overall high level of genetic diversity (87 unique PFGE patterns and 20 MLST types) among a subset of MRSP isolates tested (n = 106), certain genotypes were detected from epidemiologically connected cases at the same or different time points, suggesting persistence and/or nosocomial transmission. These results indicate a relatively high prevalence of MRS from companion animals in the Midwestern US; therefore, it is important to perform routine susceptibility testing of Staphylococcus in veterinary clinical settings for the selection of appropriate antimicrobial therapy.

Rapid Detection of Methicillin-Resistant Staphylococcus aureus Directly from Blood for the Diagnosis of Bloodstream Infections: A Mini-Review

Staphylococcus aureus represents a major human pathogen able to cause a number of infections, especially bloodstream infections (BSI). Clinical use of methicillin has led to the emergence of methicillin-resistant S. aureus (MRSA) and MRSA-BSI have been reported to be associated with high morbidity and mortality. Clinical diagnosis of BSI is based on the results from blood culture that, although considered the gold standard method, is time-consuming. For this reason, rapid diagnostic tests to identify the presence of methicillin-susceptible S. aureus (MSSA) and MRSA isolates directly in blood cultures are being used with increasing frequency to rapidly commence targeted antimicrobial therapy, also in the light of antimicrobial stewardship efforts. Here, we review and report the most common rapid non-molecular and molecular methods currently available to detect the presence of MRSA directly from blood.

Modern Tools for Rapid Diagnostics of Antimicrobial Resistance

Fast, robust, and affordable antimicrobial susceptibility testing (AST) is required, as roughly 50% of antibiotic treatments are started with wrong antibiotics and without a proper diagnosis of the pathogen. Validated growth-based AST according to EUCAST or CLSI (European Committee on Antimicrobial Susceptibility Testing, Clinical Laboratory Standards Institute) recommendations is currently suggested to guide the antimicrobial therapy. Any new AST should be validated against these standard methods. Many rapid diagnostic techniques can already provide pathogen identification. Some of them can additionally detect the presence of resistance genes or resistance proteins, but usually isolated pure cultures are needed for AST. We discuss the value of the technologies applying nucleic acid amplification, whole genome sequencing, and hybridization as well as immunodiagnostic and mass spectrometry-based methods and biosensor-based AST. Additionally, we evaluate the potential of integrated systems applying microfluidics to integrate cultivation, lysis, purification, and signal reading steps. We discuss technologies and commercial products with potential for Point-of-Care Testing (POCT) and their capability to analyze polymicrobial samples without pre-purification steps. The purpose of this critical review is to present the needs and drivers for AST development, to show the benefits and limitations of AST methods, to introduce promising new POCT-compatible technologies, and to discuss AST technologies that are likely to thrive in the future.

Novel strategies for rapid identification and susceptibility testing of MRSA

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) is associated with adverse clinical outcomes and increased morbidity, mortality, length of hospital stay, and health-care costs. Rapid diagnosis of MRSA infections has been associated with positive impact on clinical outcomes.

AREAS COVERED

We searched relevant papers in PubMed for the last 10 years. In major papers, we scanned the bibliographies to ensure that important articles were included. This review describes screening and diagnostic test methods for MRSA and their analytical performances with a focus on rapid molecular-based assays including those that are on the horizon. Future novel technologies will allow more rapid detection of phenotypic resistance. In the case of whole-genome sequencing, detection of mutations may predict resistance, transmission, and virulence.

EXPERT OPINION

Currently there are many diagnostic options for the detection of MRSA in surveillance and clinical samples. In general, these are highly accurate and have resulted in improvements in targeted management and reduction in hospital or intensive care unit length of stay for both MSSA and MRSA. Impact on mortality has been variable. Promising novel technologies will not only accurately identify pathogens and detect their resistance markers but will allow discovery of virulence determinants that might further affect patient management.

Selection and characterization of DNA aptamers for constructing colorimetric biosensor for detection of PBP2a

Rapid and accurate diagnosis of methicillin-resistant staphylococcus aureus (MRSA) is vital for patient treatment, control of infection and monitoring epidemiology. Penicillin binding proteins (PBP2a), as an important marker protein of MRSA, has been proposed as the screening test target for tolerant bacteria of MRSA. However, current technologies based on PBP2a activity or PBP2a immunoassays were suboptimal specificity and sensitivity. In this report, the selection and characterization of DNA aptamers that binds to PBP2a was described. The DNA aptamer is with high affinity and selectivity to binding with PBP2a. Furthermore, utilizing the switched mimicking peroxidase for gold nanoparticles loaded graphene oxide (GO/Au) nanomaterials based on the effect between GO/Au and DNA, a powerful strategy was set out for designing aptamer-based colorimetric biosensor for detection of PBP2a. In this strategy, the employment of biosensor based on GO/Au and PBP2a aptamer greatly improved the detection sensitivity and selectivity with limit of detection as low as 20 nM. Accordingly, the reversible nanozyme inhibition/activation approach may be universally applicable for the biomedical diagnosis.

Prediction of methicillin-resistant Staphylococcus aureus bloodstream infection: do we need rapid diagnostic tests?

Staphylococcus aureus (SA) is the leading cause of bloodstream infection (BSI). The incidence of methicillin-resistant SA (MRSA) has decreased in France and Europe since one decade. Early and precise prediction of methicillin susceptibility is needed to improve probabilistic antibiotic therapy of MRSA-BSI. The aim of this study was to identify MRSA-BSI risk factors at admission and evaluate which patients need costly rapid diagnostic tests. A single-center retrospective descriptive study of all diagnosed SA-BSI was conducted in a French University Hospital between January 2015 and December 2016. All medical charts were reviewed. Univariate and multivariate analyses by a logistic regression model were performed on the data. We then build a prediction score of MRSA-BSI by assigning one point for each of the risk factor identified. During the study period, 151 SA-BSI were identified including 32 (21%) MRSA-BSI. In multivariate analysis, three factors were associated with MRSA-BSI: coming from long-term care facility, known previous MRSA colonization and/or infection, and chronic renal disease. Among our population, respectively, 5% and 100% had a MRSA-BSI when no or three risk factors were identified. Therefore, among the PCR performed, 43 (96%) could be avoided according to our clinical score. In our study, methicillin-susceptible SA and MRSA-BSI can be predictable by counting MRSA risk factors. This prediction rule could avoid the use of expensive rapid diagnostic tests. Prospective studies and prediction rules could help physicians to predict SA-BSI susceptibility to improve appropriate empiric therapy choice.

Evaluation of the ePlex Blood Culture Identification Panels for Detection of Pathogens in Bloodstream Infections

Rapid identification and susceptibility testing results are of importance for the early appropriate therapy of bloodstream infections. The ePlex (GenMark Diagnostics) blood culture identification (BCID) panels are fully automated PCR-based assays designed to identify Gram-positive and Gram-negative bacteria, fungi, and bacterial resistance genes within 1.5 h from positive blood culture.

Rapid identification and susceptibility testing results are of importance for the early appropriate therapy of bloodstream infections. The ePlex (GenMark Diagnostics) blood culture identification (BCID) panels are fully automated PCR-based assays designed to identify Gram-positive and Gram-negative bacteria, fungi, and bacterial resistance genes within 1.5 h from positive blood culture. Consecutive non-duplicate positive blood culture episodes were tested by the ePlex system prospectively. The choice of panel(s) (Gram-positive, Gram-negative, and/or fungal pathogens) was defined by Gram-stained microscopy of blood culture-positive bottles (BacT/Alert; bioMérieux). Results with the ePlex panels were compared to the identification results obtained by standard culture-based workflow. In total, 216 positive blood culture episodes were evaluable, yielding 263 identification results. The sensitivity/positive predictive value for detection by the ePlex panels of targeted cultured isolates were 97% and 99% for the Gram-positive panel and 99% and 96% for the Gram-negative panel, resulting in overall agreement rates of 96% and 94% for the Gram-positive and Gram-negative panel, respectively. All 26 samples with targeted resistance results were correctly detected by the ePlex panels. The ePlex panels provided highly accurate results and proved to be an excellent diagnostic tool for the rapid identification of pathogens causing bloodstream infections. The short time to results may be of added value for optimizing the clinical management of patients with sepsis.

The management and outcomes of Staphylococcus aureus bacteraemia at a South African referral hospital: A prospective observational study

OBJECTIVES

Data on the management and outcomes of Staphylococcus aureus bacteraemia (SAB) in resource-limited settings are limited. The aim of this study was to describe a cohort of South African patients with SAB, and explore the factors associated with complicated infection and death.

METHODS

This was a prospective observational study of patients over the age of 13 years admitted to a South African referral hospital with SAB.

RESULTS

One hundred SAB infection episodes occurring in 98 patients were included. SAB was healthcare-associated in 68.4%; 24.0% of all cases were caused by methicillin-resistant S. aureus (MRSA). Ninety-day mortality was 47.0%, with 83.3% of deaths attributable to SAB. There was a trend towards increased 90-day mortality with MRSA infection (odds ratio (OR) 1.28, 95% confidence interval (CI) 1.0-15.1) and the presence of comorbidities (OR 4.1, 95% CI 1.0-21.6). The risk of complicated infection was higher with non-optimal definitive antibiotic therapy (OR 8.5, 95% CI 1.8-52.4), female sex (OR 3.8, 95% CI 1.1-16.3), and community-acquired infection (OR 7.4, 95% CI 2.0-33.1). Definitive antibiotic therapy was non-optimal in 22.6% of all cases.

CONCLUSIONS

SAB-related mortality was high. A large proportion of cases may be preventable, and there is a need for improved antibiotic management.

An Automated Sample Preparation Instrument to Accelerate Positive Blood Cultures Microbial Identification by MALDI-TOF Mass Spectrometry (Vitek®MS)

Sepsis is the leading cause of death among patients in intensive care units (ICUs) requiring an early diagnosis to introduce efficient therapeutic intervention. Rapid identification (ID) of a causative pathogen is key to guide directed antimicrobial selection and was recently shown to reduce hospitalization length in ICUs. Direct processing of positive blood cultures by MALDI-TOF MS technology is one of the several currently available tools used to generate rapid microbial ID. However, all recently published protocols are still manual and time consuming, requiring dedicated technician availability and specific strategies for batch processing. We present here a new prototype instrument for automated preparation of Vitek^®MS slides directly from positive blood culture broth based on an “all-in-one” extraction strip. This bench top instrument was evaluated on 111 and 22 organisms processed using artificially inoculated blood culture bottles in the BacT/ALERT^® 3D (SA/SN blood culture bottles) or the BacT/ALERT Virtuo^TM system (FA/FN Plus bottles), respectively. Overall, this new preparation station provided reliable and accurate Vitek MS species-level identification of 87% (Gram-negative bacteria = 85%, Gram-positive bacteria = 88%, and yeast = 100%) when used with BacT/ALERT^® 3D and of 84% (Gram-negative bacteria = 86%, Gram-positive bacteria = 86%, and yeast = 75%) with Virtuo^® instruments, respectively. The prototype was then evaluated in a clinical microbiology laboratory on 102 clinical blood culture bottles and compared to routine laboratory ID procedures. Overall, the correlation of ID on monomicrobial bottles was 83% (Gram-negative bacteria = 89%, Gram-positive bacteria = 79%, and yeast = 78%), demonstrating roughly equivalent performance between manual and automatized extraction methods. This prototype instrument exhibited a high level of performance regardless of bottle type or BacT/ALERT system. Furthermore, blood culture workflow could potentially be improved by converting direct ID of positive blood cultures from a batch-based to real-time and “on-demand” process.

Molecular Detection of Methicillin-Resistant Staphylococcus aureus by Non-Protein Coding RNA-Mediated Monoplex Polymerase Chain Reaction

Non-protein coding RNA (npcRNA) is a functional RNA molecule that is not translated into a protein. Bacterial npcRNAs are structurally diversified molecules, typically 50-200 nucleotides in length. They play a crucial physiological role in cellular networking, including stress responses, replication and bacterial virulence. In this study, by using an identified npcRNA gene (Sau-02) in Methicillin-resistant Staphylococcus aureus (MRSA), we identified the Gram-positive bacteria S. aureus. A Sau-02-mediated monoplex Polymerase Chain Reaction (PCR) assay was designed that displayed high sensitivity and specificity. Fourteen different bacteria and 18 S. aureus strains were tested, and the results showed that the Sau-02 gene is specific to S. aureus. The detection limit was tested against genomic DNA from MRSA and was found to be ~10 genome copies. Further, the detection was extended to whole-cell MRSA detection, and we reached the detection limit with two bacteria. The monoplex PCR assay demonstrated in this study is a novel detection method that can replicate other npcRNA-mediated detection assays.